The invention concerns generally the technological field of planar antenna arrangements in portable radio devices. Especially but not exclusively the invention concern s inverted-F antenna arrangements. The invention also concerns a portable radio device equipped with such a planar antenna arrangement. And, additionally the invention concerns a method for assembling and testing a portable radio device comprising a planar antenna.
Low profile antennas such as planar antennas are well known in the art. One of the known and widely applicable planar antenna solutions used in mobile telephones is the PIFA or Planar Inverted F Antenna. It consists of a planar conductive sheet (that may have a smooth outer contour or comprise various cuts) that acts as a radiator, and a planar conductive ground surface which is essentially parallel to the radiator. The surfaces need not be exactly planar, and they need not be exactly parallel to each other. There are one or a few conductive connections between the radiator and the ground surface, usually implemented as conductive pins or strips that are essentially perpendicular to the direction of the planar surfaces. A feeding pin or a feeding strip coupled to a certain feeding point of the planar radiator serves to couple the antenna to the antenna port of a radio device.
An example of an inverted-F antenna is shown in FIG. 1 of the accompanying drawings. The antenna 10 comprises a feed section 12 coupled to a short circuited inductive stub 14 and a capacitive line 16. The inductive stub 14 is short circuited to a ground plane 18, above which the feed section 12 protrudes by a distance D. The ground plane 18 is open to allow access for the feed section 12 which is electrically isolated from 11 from the ground plane 18. The respective lengths L1, L2, of the inductive stub 14 and the capacitive line 16 are determined to give a desired resonanc e frequency and input impedance Zin seen from the antenna feed point 12. The input impedance is dependant upon the position of the feed section 12 and hence the lengths L1 and L2, a nd can be made substantially resistive. Further details regarding inverted-L or -F antennas may be found in xe2x80x9cSmall Antennasxe2x80x9d ISBN 0863 80 048 3, pages 1116-151.
Inverted F-antenna s have found particular applications in the portable radio devices, and especially mobile telephones where their high gain and omni-directional radiation patterns are particularly suitable. They are also suitable in applications where good frequency selectivity is required. Additionally, since the antennas are relatively small at typical radio telephone frequencies they can be incorporated within the housing of a radio telephone thereby not interfering with the overall aesthetic appeal of the radio telephone and giving it a more attractive appearance than radio telephones having external antennas. By placing the antenna inside the housing of a radio telephone, the antenna is also less likely to be damaged and therefore have a longer life time. The ground plane of an inverted-F antenna can be made on a printed wired board, and thus the inverted-F antenna lends itself to planar fabrication on printed wired board typically used in radio telephones.
FIG. 2 illustrates a known PIFA construction and its use in a mobile telephone, which in FIG. 1 is seen in an opened position so that its keypad, display, microphone and loudspeaker which are located on the distant side of the right-hand part are not seen. The functional parts of the mobile telephone 201 have been constructed onto a printed wired board or PWB 202. The PWB with all the components attached thereto has been enclosed into an outer cover 203 which consists of two halves 203a and 203b and also serves as a support structure. The PWB 202 is attached to the front half 203a of the outer cover. At the top end of the PWB 202 there is an antenna feeding pad 204 and a ground plane 205 which are parts of the conductive structures formed on the planar surface of the PWB. In most mobile telephones and other small radio devices the PWB is of the multilayer type in which case the ground plane 205 could be also located at one of the inner layers.
At the top end of the inside of the cover there is a conductive radiator 206. A feeding pin 207 and a grounding pin 208 protrude from the conductive radiator 206 into a direction which is towards the PWB 202 when the parts 206, 103a and 103b are attached together. When the cover is closed, the conductive radiator 206 and the ground plane 205 come into a parallel configuration and the feeding pin 207 and grounding pin 208 touch the antenna feeding pad 204 and ground plane 205 respectively, so a PIFA antenna is produced. The back cover 203b must be electrically non-conductive at least at its top end where the conductive radiator 206 is located.
Despite the small size of planar antennas, the fact that radio telephones are becoming smaller and smaller and more complex necessitating a greater amount of electronics within the housing, the space available for the inverted-F antenna is getting smaller and it is more difficult to conviniently fit such antennas into the housing.
Another problem with using an inverted-F antenna is related to manufacturing and especially testing the radio device. The testing phase of a radio telephone normally comprises alignment and galvanically measured tests of the RF electronics. This is normally made before the antenna is assembled by connecting an RF test probe in contact points of the antenna. After this phase of testing the RF test probe is disconnected and the antenna is assembled and connected in place. Finally, the function of the antenna is tested using a coupler. In a mass production of radio devices such as radio telephones it is advatageous to use automated assembling and testing. Therefore it is a drawback that the RF electronics and the antenna must be tested separately having an assembly phase between the test phases. Therefore, in an automated manufacturing the radio telephone should be first placed on an automated assembly line for assembling the electronics, then on an automated testing bench for testing the (RF) electronics, and after testing the electronics the equipment should be placed on a next assembly line for assembling the antenna, and finally the equipment should be again placed on a test bench for testing the antenna. Having so many assembling/testing phases causes additional time and costs for the manufacturing of radio telephones.
It is an object of the present invention to provide a planar antenna structure with which the disadvantages of prior art solutions would be reduced or avoided. It is especially an object of the present invention that the antenna structure is applicable to large scale mass production of radio devices, including testing.
One idea of the present invention is providing an aperture in the radiator plate of the planar antenna. An RF test point is provided for aligning the RF electronics and the RF test point is located in such a way related to the aperture of the radiator that the test signal is easily led through the aperture. It is further advantageous that an RF switch is provided for coupling/decoupling a connection between the planar antenna and the RF electronics. In a preferred embodiment the RF switch is integrated with the RF test point. The inventive arrangement thus allows testing the RF electronics after the radiator plate has been attached to the PWB.
The present invention has important advantages over the prior art. The tuning and testing of the radio device can be made with a single automatic arrangement, and it is necessary to attach the device to the test bench just once. It is also possible to make the automatic assembly work on a single line before the testing/tuning procedure; It is not necessary to make any substantial assembly work after the testing/tuning procedure. As a result, it is possible by using the present invention to provide assembly and testing procedures where substantially all assembly work can be done without intermediate testing phases and all testing can be done without intermediate assembly phases.
If the aperture is a hole, ie. it is bordered by the radiator element of the antenna, the hole does not have a significant negative effect on the radiation properties of the antenna. However, placing the RF switch and test point under the radiator element saves space on the printed wired board and the radio device such as radio telepone can be designed smaller.
The antenna circuit arrangement according to the invention comprises
a planar antenna with a ground plane and a planar radiator element and disposed substantially parallel to the ground plane, and
an RF circuit coupled to the planar antenna for processing RF signals received by the planar antenna and/or RF signals to be transmitted by the antenna. It is characterized in that
the antenna circuit arrangement comprises a test point for connecting a test signal to/from the RF circuit, and
an aperture in the planar radiator element for conveying said test signal through said aperture.
The invention applies also to a portable radio device comprising an antenna arrangement, and further comprising
a planar antenna with a ground plane and a planar radiator element and disposed substantially parallel to the ground plane, and
an RF circuit coupled to the planar antenna for processing RF signals received by the planar antenna and/or RF signals to be transmitted by the antenna. It is characterized in that
the antenna circuit arrangement comprises a test point for connecting a test signal to/from the RF circuit, and
an aperture in the planar radiator element for conveying said test signal through said aperture.
The invention also concerns a method for assembling and testing an antenna arrangement including a planar antenna and RF electronics, the planar antenna comprising a ground plane and a planar radiator, wherein
the RF electronics is assembled,
the planar radiator is attached to the RF electronics assembly,
the RF electronics is tested by connecting a test signal to/from the RF-electronics which is decoupled from the planar antenna,
the planar planar antenna is coupled to the RF electronics, and
the planar antenna is tested when the planar antenna is coupled to the RF electronics. It is characterized in that in said step of testing the RF electronics a test signal is conveyed through an aperture of the radiator plane of the planar antenna to/from a test point of the RF electronics.
Definitions xe2x80x9cradiator planexe2x80x9d and xe2x80x9cradiator elementxe2x80x9d are used here, but these definitions are not meant to restrict the function of the element of the antenna to RF transmission, but the definition also includes elements of antennas that are used for RF reception.